Low- and high-volume blood-flow restriction treadmill walking both improve maximal aerobic capacity independently of...

Assess the effect of low- and high-volume blood flow restriction training (BFR) on maximal aerobic capacity (VO₂ max) and determine if alteration in VO₂ max is mediated through changes in hemoglobin mass (Hbmass) and blood volume.

Participants' Hb_mass (CO-rebreathe), single, and double-leg VO₂ max and blood volume regulating hormonal responses (renin and copeptin) were measured before and after BFR training. Training consisted of treadmill walking either (1) twice-daily for 4week (CON and BFR_HV ) or (2) twice-weekly for 6week (BFR_LV ). Each session consisted of five intervals (3 min, 5% incline, 5 km/h, 100% of lowest occlusion pressure), with 1 min of standing rest between sets.

VO₂ max increased using both training exposures, in as quickly as 2-weeks (BFR_LV baseline to 4week: +315 ± 241 mL (8.7%), p = 0.02; BFR_HV baseline to 2week: +360 ± 261 mL (7.9%), p < 0.01), for the BFR_LV and BFR_HV groups, with no change in CON. Single- and double-leg VO₂ max improved proportionately (single/double-leg VO₂ max ratio: BFR_LV 78 ± 4.9-78 ± 5.8%, BFR_HV 79 ± 6.5-77 ± 6.5%), suggesting that the mechanism for increased VO₂ max is not solely limited to central or peripheral adaptations. Hb_mass remained unchanged across groups (CON: +10.2 ± 34 g, BFR_LV : +6.6 ± 42 g, BFR_HV : +3.2 ± 44 g; p = 0.9), despite a significant release of blood volume regulating hormones after initial BFR exposure (renin +20.8 ± 21.9 ng/L, p < 0.01; copeptin +22.0 ± 23.8 pmol/L, p < 0.01), which was blunted following BFR_HV training (renin: +13.4 ± 12.4 ng/L, p = 0.09; copeptin: +1.9 ± 1.7 pmol/L, p = 0.98).

BFR treadmill walking increases VO₂ max irrespective of changes in Hb_mass or blood volume despite a large release of blood volume regulating hormones in response to BFR treadmill walking.